The effect of the calcium antagonist isradipine on serotonin metabolism and platelet aggregation was studied in 17 patients with essential hypertension. Platelet serotonin content, plasma serotonin, 5-hydroxyindoleacetic acid levels, and platelet aggregation [induced ex vivo by serotonin and low-density lipoprotein (LDL)] were measured after a 4-week placebo period and after 12 weeks of oral treatment with isradipine. Isradipine treatment significantly inhibited platelet aggregation induced by LDL and serotonin; the amplifying effect of LDL on serotonin-induced aggregation seen with placebo was not observed after 12 weeks of treatment with isradipine. Platelet serotonin content increased significantly during isradipine treatment; this increase was inversely related to the pretreatment content of serotonin in platelets. The results indicate that treatment with isradipine restores the impaired handling of platelet serotonin as well as the platelet response to serotonin and LDL in hypertensive patients. This effect of isradipine may be regarded as one of the cellular mechanisms of thrombovascular protection and may be of clinical significance in terms of platelet and vessel wall interaction.

Department of Clinical Pharmacology Institute of Preventive and Clinical Medicine Bratislava Czechoslovakia